Abstract:

The present invention relates to a thermoacoustic device that includes an
acoustic element. The acoustic element includes a substrate, a plurality
of microspaces, and a metal film. The metal film is located above the
substrate. A plurality of microspaces is defined between the substrate
and the metal film. The metal film is partially suspended above the
substrate.

Claims:

1. A thermoacoustic device, the thermoacoustic device comprising:an
acoustic element, the acoustic element comprising,a substrate; anda metal
film located above the substrate, wherein a plurality of microspaces is
defined between the substrate and the metal film, whereby the metal film
is suspended above the substrate.

2. The thermoacoustic device as claimed in claim 1, further comprising a
signal input device, wherein the signal input device is electrically
connected to the metal film.

3. The thermoacoustic device as claimed in claim 2, further comprising at
least two electrodes electrically connected to the metal film, wherein
the at least two electrodes are electrically connected to the signal
input device.

4. The thermoacoustic device as claimed in claim 1, further comprising at
least two electrodes electrically connected to the metal film, wherein
the at least two electrodes are spaced apart from each other and disposed
on the metal film.

5. The thermoacoustic device as claimed in claim 1, wherein heat capacity
per unit area of the metal film is less than or equal to
2.times.10.sup.-4 J/cm2*K.

6. The thermoacoustic device as claimed in claim 1, wherein the metal film
comprises a material selected from the group consisting of iron, nickel,
gold, copper, silver, cobalt, platinum, aluminum and any combination
thereof.

7. The thermoacoustic device as claimed in claim 1, wherein a thickness of
the metal film is less than 0.7 μm.

8. The thermoacoustic device as claimed in claim 1, wherein the
microspaces are defined where the substrate is in contact with the metal
film.

9. The thermoacoustic device as claimed in claim 8, wherein contact area
of each contact point between the substrate and the metal film is less
than or equal to 1 mm.sup.2.

10. The thermoacoustic device as claimed in claim 8, wherein a distance of
two adjacent contact points between the metal film and the substrate is
less than or equal to 1 mm.

11. The thermoacoustic device as claimed in claim 1, wherein a plurality
of particles is distributed on the substrate to form the microspaces
between the substrate and the metal film.

12. The thermoacoustic device as claimed in claim 11, wherein the acoustic
element further comprises an adhesive layer disposed on the substrate for
fixing the particles.

13. The thermoacoustic device as claimed in claim 11, wherein the
particles comprise of a thermal insulating material.

14. The thermoacoustic device as claimed in claim 13, wherein the
particles comprises a material selected from the group consisting of
glass, quartz, ceramic and any combination thereof.

15. The thermoacoustic device as claimed in claim 11, wherein the diameter
of the particles is less than or equal to 1 mm.

16. A thermoacoustic device, comprising:a signal input device;a substrate
comprising a plurality of microstructures on a surface thereof; anda
metal film suspended above the surface of the substrate and electrically
connected to the signal input device, and the metal film is capable of
generating sounds in response to inputs from the signal input device.

17. The thermoacoustic device as claimed in claim 16, wherein the
microstructures are microspaces defined at the surface of the substrate.

18. The thermoacoustic device as claimed in claim 16, wherein the
microstructures are particles located on the surface of the substrate.

19. The thermoacoustic device as claimed in claim 16, wherein heat
capacity per unit area of the metal film is less than or equal to
2.times.10.sup.-4 J/cm2*K.

20. The thermoacoustic device as claimed in claim 16, wherein a thickness
of the metal film is less than 0.7 μm.

[0003]The present disclosure relates to thermoacoustic devices, and
particularly to a metal material based thermoacoustic device.

[0004]2. Description of Related Art

[0005]A thermophone based on the thermoacoustic effect was created by H.
D. Arnold and I. B. Crandall (H. D. Arnold and I. B. Crandall, "The
thermophone as a precision source of sound", Phys. Rev. 10, pp 22-38
(1917)). The thermophone uses a platinum strip with a thickness of
7×10-5 cm as a thermoacoustic element. When signals are input
into the platinum strip, heat is produced in the platinum strip according
to the variations of the signal and/or signal intensity. Heat is
propagated into the surrounding medium. The heat in the medium causes
thermal expansion and contraction, and produces pressure waves in the
surrounding medium, resulting in sound wave generation. The thermophone
includes the platinum strip, clamps, and an electrical signal input
device. The clamps are spaced apart from each other and are disposed on
two ends of the platinum strip. The clamps are used for fixing the
platinum strip. The middle region of the platinum strip is suspended
while the two ends of the platinum strip are fixed. However, a suspending
metal slice with thickness smaller than 7×10-5 centimeter (cm)
is difficult to fabricate as a result of restriction of fabrication
technology, thus, a smaller heat capacity per unit area of the metal
slice cannot be achieved, which leads to sounds extremely weak because
the heat capacity per unit area of the metal slice is too high.

[0006]What is needed, therefore, is to provide a thermoacoustic device
having a high acoustic intensity.

BRIEF DESCRIPTION OF THE DRAWINGS

[0007]Many aspects of the embodiments can be better understood with
reference to the following drawings. The components in the drawings are
not necessarily drawn to scale, the emphasis instead being placed upon
clearly illustrating the principles of the embodiments. Moreover, in the
drawings, like reference numerals designate corresponding parts
throughout the several views.

[0008]FIG. 1 is a structural schematic view of an embodiment of a
thermoacoustic device.

[0009]FIG. 2 is a flow chart of a method for making the thermoacoustic
device.

[0010]FIG. 3 shows sectional views at various stages of making the
thermoacoustic device of FIG. 1.

[0011]FIG. 4 is a structural schematic view of another embodiment of a
thermoacoustic device.

DETAILED DESCRIPTION

[0012]The disclosure is illustrated by way of example and not by way of
limitation in the figures of the accompanying drawings in which like
references indicate similar elements. It should be noted that references
to "an" or "one" embodiment in this disclosure are not necessarily to the
same embodiment, and such references mean at least one.

[0013]Referring to FIG. 1, a thermoacoustic device 10 of an embodiment
includes a signal input device 12, an acoustic element 14, and at least
two electrodes 18.

[0014]The acoustic element 14 includes a substrate 16, a plurality of
microstructures 17, and a metal film 15. The substrate 16 has a surface
162. The microstructures 17 are disposed on the surface 162. The metal
film 15 is disposed on the plurality of microstructures 17. The
electrodes 18 are spaced from each other and electrically connected to
the metal film 15 and the signal input device 12. The electrodes 18 are
used for inputting electrical signals into the acoustic element 14. The
electrical signals are produced by the signal input device 12. The
electrodes 18 and the signal input device 12 can be electrically
connected together by a wire 19.

[0015]The substrate 16 functions as a supporting structure for supporting
the microstructures 17 and the metal film 15. The shape of the substrate
16 is not limited. In one embodiment, the surface 162 has many tiny bumps
that serve as the microstructures 17. The metal film 15 is disposed on
the bumpy surface 162. The substrate 16 can be made of a rigid or
flexible insulating material, and the material of the substrate 16 has a
good thermal insulating property, thereby preventing the substrate 16
from absorbing the heat generated by the metal film 15. In some
embodiments, the substrate 16 can be made of diamond, glass, quartz,
plastic, or resin et al.

[0016]When a signal with great intensity is inputted the metal film 15
with a small thickness, the metal film 15 is easy to be broken because
the signal with great intensity can create great heat in the metal film
15. The great heat will cause thermal expansion in the metal film 15,
which make the metal film 15 with small thickness break. The plurality of
microstructures 17 can support the metal film 15 to avoid the breaking of
the metal film 15. Contact area of the metal film 15 with each
microstructure/bump 17 can be less than or equal to 1 square millimeter
(mm2). About 10 to about 99 percent by area of the metal film 15 is
suspended. Therefore, the metal film 15 can have a great contact area
with the surrounding medium (e.g., air) and great thermal transmittance
area, thereby improving acoustic effect of the thermoacoustic device 10.
Distance of two adjacent contact positions between the metal film 15 and
the microstructures 17 can be less than or equal to 1 mm, so that the
metal film 15 can be uniformly supported by the microstructures 17, and
will not be distorted under the weight of itself. The metal film 15 is
supported by the microstructures 17. Therefore, signals can be input to
the metal film 15 with great intensity without breaking the metal film
15, thereby making a sound with great acoustic intensity.

[0017]The metal film 15 can be made of a kind of material with a small
heat capacity per unit area and good ductility, such as iron (Fe), nickel
(Ni), gold (Au), copper (Cu), silver (Ag), cobalt (Co), platinum (Pt),
aluminum (Al) or any combination thereof. The metal film 15 is supported
by the microstructures 17, thus, the thickness of the metal film 15 can
be extremely thin and have an extremely small heat capacity per unit
area. In use of the thermoacoustic device 10, the metal film 15 is not
easily broken, and can make sounds at a variety of frequencies and high
intensity. In one embodiment, the thickness of the metal film 15 can be
less than 0.7 μm, the heat capacity per unit area of the metal film 15
can be less than 2×10-4 J/cm2*K. The heat capacity per
unit area of the metal film 15 is not only related to the material of the
metal film 15 but also the thickness of the metal film 15. The thinner
the metal film 15, the less the heat capacity per unit area of the metal
film 15. The frequency and the intensity of the sound produced by the
metal film 15 are related to the heat capacity per unit area of the metal
film 15. The smaller the heat capacity per unit area, the wider the
frequency range of the sound that can be produced by the metal film 15,
and the higher the intensity of the sound.

[0018]The electrodes 18 are made of conductive material. The shape of the
electrodes 18 is not limited and can have, for example, a lamellar, rod,
wire, or block like structure. The material of the electrodes 18 can be
metal, conductive adhesive, carbon nanotubes, or indium tin oxides among
other conductive materials. In one embodiment, the electrodes 18 are
metal rods. The electrodes 18 are configured to electrically connect the
signal input device 12 to the acoustic element 14. The electrodes 18 are
spaced apart from each other and disposed on the surface of the metal
film 15. A conductive adhesive can be further provided between the
electrodes 18 and the metal film 15. The conductive adhesive can be used
to better secure and provide for electrical contact between the
electrodes 18 and the metal film 15. The conductive adhesive can be
silver paste. In one embodiment, the length of the electrodes 18 is equal
to the width of the metal film 15, in order that audio signals are
transferred to the whole metal film 15. In addition, the electrodes 18
can be optional, the signal input device 12 can directly and electrically
connect to the metal film 15, thereby directly inputting the audio
signals into the metal film 15.

[0019]In one embodiment, the signal input device 12 is electrically
connected to the electrodes 18 by the wire 19, and inputs audio signals
into the acoustic element 14 via the electrodes 18. The audio signals are
conducted from one electrode 18 to the other electrode 18 in the metal
film 15.

[0020]The metal film 15 has a small thickness, extremely small heat
capacity per unit area, and a large specific surface area that make the
metal film 15 emit sound audible to humans. In use of the thermoacoustic
device 10, variable heat waves are produced in the metal film 15
according to the variations of the signal and/or signal strength.
Meanwhile, the metal film 15 exchanges heat with the surrounding medium.
The variable heat waves transmitted to the medium causes thermal
expansion and contraction of the medium, and thus, produces pressure
waves in the surrounding medium. The pressure waves result in sound wave
generation. The sounds may have a wide frequency range from about 20 Hz
to about 100 KHz, and sound pressure levels greater than 60 dB. The total
harmonic distortion of the metal film 15 is extremely small, thus the
thermoacoustic device 10 has extensive application possibilities. In one
embodiment, the metal film 15 is supported by the substrate 16 and the
microstructures 17, thus the metal film 15 is not easily distorted and
broken, and can receive signals with high intensity. The life of the
metal film 15 is relatively long.

[0021]Referring to FIGS. 2 and 3, in one embodiment, a method for making
the thermoacoustic device 10 is provided, the method includes:

(a) providing a substrate 16, having a surface 162, and a signal input
device 12;(b) forming a plurality of microstructures 17 on the surface
162 of the substrate 16;(c) fabricating a sacrifice layer 13 to fill in
spaces between the microstructures 17;(d) depositing a metal film 15 on a
top surface of the sacrifice layer 13;(e) removing the sacrifice layer
13; and(f) electrically connecting the signal input device 12 with the
acoustic element 14.

[0022]In step (b), the microstructures 17 are made by disposing the
surface 162 to form a plurality of small bumps, by using a method of
photo etching, ion beam etching, electron beam etching, sand blasting,
milling or screen printing.

[0023]In step (c), the sacrifice layer 13 can be removed by heating or
etching. The sacrifice layer 13 can be made of organic material with a
low decomposing temperature. The decomposing temperature should be less
than melting point of the metal film 15. In one embodiment, the sacrifice
layer 13 is made of organic material that is completely decomposed below
450 degrees, such as acrylic resin or guncotton. The thickness of the
sacrifice layer 13 can be less than the height of the microstructures 17.

[0024]The method for forming the sacrifice layer 13 can include steps of:

(S1) providing an organic polymer solution confected with polymer,
plasticizing agent, and solvent or cosolvent proportionally.(S2) coating
the organic polymer solution on the surface 162 of the substrate 16;
and(S3) let standing for a while to solidify the organic polymer
solution, thereby forming the sacrifice layer 13.

[0025]In step (S1), the polymer can include poly (isobutyl methacrylate)
and crylic acid B-72 resin. The plasticizing agent can include dibutyl
phthalate (DBP). The solvent can include ethyl acetate and butyl acetate.
The cosolvent can include ethanol and butanol. In one embodiment, the
polymer solution is confected according to table 1.

[0026]In step (S2), the coating technology can be manual or automatic.
Furthermore, before coating the polymer solution, the substrate 16 can be
soaked in water for about 1 minute to about 10 minutes, therefore, the
surface tension of the surface 162 can be decreased, so that the polymer
solution can be easily spread on the surface 162. The top surface of the
sacrifice layer 13 can be polished smooth.

[0027]In step (d), the metal film can be made by vacuum evaporation, or
magnetron sputtering. Therefore, a very thin metal film can be formed on
the top surface of the sacrifice layer 13.

[0028]In step (e), in the process of decomposing of the sacrifice layer
13, the metal film 15 gradually descends under force of gravity to
contact with the microstructures 17. When the sacrifice layer 13 is
removed by heating, the metal film 15 and the substrate 16 should not be
melted to integrate with each other. The decomposing temperature of the
sacrifice layer 13 is less than the melting point of the metal film 15
and the substrate 16. When the sacrifice layer 13 is completely
decomposed, the metal film 15 is suspended above the surface 162 of the
substrate 16 by supporting of the microstructures 17. The resulting
structure will provide for a metal film 15 having a great contact area
with the air or other surrounding medium.

[0029]Furthermore, the electrodes 18 can be provided, the electrodes 18
can be adhered on surface of the metal film 15 by conductive adhesive and
spaced apart from each other.

[0030]In step (f), the signal input device 12 can be a device such as an
MP3 player, or power amplifier. The signal input device 12 can be
directly and electrically connected to the metal film 15 by a conductive
wire, or indirectly and electrically connected to the metal film 15 by
electrodes 18. The signal input device 12 is electrically connected to
the electrodes 18 by the wire 19.

[0031]In one embodiment, after the sacrifice layer 13 is decomposed, the
metal film 15 is suspended above the surface 162 of the substrate 16 and
supported by the microstructures 17. The metal film 15 can be a
free-standing structure, the term "free-standing" includes, but is not
limited to, a structure that does not have to be supported by a substrate
and can sustain the weight of itself when it is hoisted by a portion
thereof without any significant damage to its structural integrity. A
portion of the metal film 15 is supported by the microstructures 17, and
the rest of the metal film 15 is suspended between the microstructures
17. The metal film 15 previously supported by the sacrifice layer 13
settles to contact with and be supported by the microstructures 17 after
the sacrifice layer 13 is removed. This method can prevent any damage of
the extremely thin metal film 15 during the processing and leave a
free-standing metal film 15 on the substrate 16. Microspaces are defined
between the surface 162 and the metal film 15. The thinner the metal film
15, the smaller the heat capacity per unit area of the metal film 15. In
one embodiment, the metal film 15 is extremely thin, the heat capacity
per unit area of the metal film 15 is extremely small, and sound caused
by the metal film 15 has a wide frequency and a great intensity. The
microstructures 17 can support the metal film 15 to avoid damage,
meanwhile, the metal film 15 has a great thermal transmittance area and
can create sound with an ideal acoustic quality.

[0032]Referring to FIG. 4, another embodiment of a thermoacoustic device
20 includes a signal input device 22, an acoustic element 24, and at
least two electrodes 28. The acoustic element 24 includes a substrate 26,
a plurality of microstructures 27, and a metal film 25. The substrate 26
has a surface 262. The microstructures 27 are disposed on the surface
262. The metal film 25 is disposed on the microstructures 27. The
electrodes 28 are spaced from each other and electrically connected to
the metal film 25. The electrodes 28 are electrically connected to the
signal input device 22 by an wire 29. The electrodes 28 are used for
inputting electrical signals into the acoustic element 24. The electrical
signals are produced by the signal input device 22.

[0033]The plurality of microstructures 27 are a plurality of particles,
and the metal film 25 is disposed on the plurality of particles.

[0034]The particles are dispersed on the surface 262 of the substrate 26.
The diameter of the particles is less than or equal to 1 mm. The material
of the particles is not limited. The particles can be made of rigid and
thermally insulating material such as glass, quartz, or ceramic, thereby
preventing the particles from absorbing heat generated by the metal film
25. An adhesive layer can be further disposed on the surface 262 of the
substrate 26, and used for adhering and fixing the particles. The
material of the adhesive layer is not limited.

[0035]In one embodiment, a method for making the acoustic device 20 is
provided, the method includes:

(a) providing a substrate 26 having a surface 262;(b) forming a plurality
of microstructures 27 on the surface 262 of the substrate 26;(c)
fabricating a sacrifice layer to fill in spaces between the
microstructures 27;(d) depositing a metal film 25 on surface of the
sacrifice layer;(e) removing the sacrifice layer; and(f) electrically
connecting a signal input device 22 to the acoustic element 24.

[0036]In step (b), the microstructures 27 are particles, the method for
forming the particles can include: (S1) coating an adhesive layer on the
surface 262 of the substrate 26; and (S2) fixing the microstructures 27
on the adhesive layer. The step (S2) can further include: providing a
plurality of particles; and uniformly allocating the particles on the
adhesive layer, thereby forming a plurality of microstructures 27.

[0037]The metal film can be supported by the microstructures and the
substrate, thus, the metal film can be extremely thin, and the metal film
can receive signals with great intensity, without being broken. The
thickness of the metal film can be less than or equal to 0.7 μm, the
heat capacity per unit area of the metal film is less than or equal to
2×10-4 J/cm2*K, thus the sound introduced by the metal
film has a wide frequency range and great intensity. The metal film is
suspended above but in contact with very little of the surface of the
substrate, thus, the metal film has a great contact area with the
surrounding medium. In use of the thermoacoustic device, the metal film
has a rapid heat exchange with surrounding medium, the heating of the
medium causes thermal expansion and contraction, and produces pressure
waves in the surrounding medium, resulting in sound wave generation.

[0038]It is to be understood, however, that even though numerous
characteristics and advantages of the present embodiments have been set
forth in the foregoing description, together with details of the
structures and functions of the embodiments, the disclosure is
illustrative only, and changes may be made in detail, especially in
matters of shape, size, and arrangement of parts within the principles of
the disclosure to the full extent indicated by the broad general meaning
of the terms in which the appended claims are expressed.

[0039]Depending on the embodiment, certain of the steps of methods
described may be removed, others may be added, and the sequence of steps
may be altered. It is also to be understood that the description and the
claims drawn to a method may include some indication in reference to
certain steps. However, the indication used is only to be viewed for
identification purposes and not as a suggestion as to an order for the
steps.